Uncontrolled cell proliferation is the hallmark of cancer. Cancerous tumor cells typically have some form of damage to the genes that directly or indirectly regulate the cell-division cycle.
Cyclin-dependent kinases (CDKs) are enzymes which are critical to cell cycle control. See, e.g., Coleman et al., “Chemical Inhibitors of Cyclin-dependent Kinases,” Annual Reports in Medicinal Chemistry, vol. 32, 1997, pp. 171-179. These enzymes regulate the transitions between the different phases of the cell cycle, such as the progression from the G1 phase to the S phase (the period of active DNA synthesis), or the progression from the G2 phase to the M phase, in which active mitosis and cell-division occurs. See, e.g., the articles on this subject appearing in Science, vol. 274, Dec. 6, 1996, pp 1643-1677.
CDKs are composed of a catalytic CDK subunit and a regulatory cyclin subunit. The cyclin subunit is the key regulator of CDK activity, with each CDK interacting with a specific subset of cyclins: e.g. cyclin A (CDK1, CDK 2). The different kinase/cyclin pairs regulate progression through specific stages of the cell cycle. See, e.g., Coleman, supra.
Aberrations in the cell cycle control system have been implicated in the uncontrolled growth of cancerous cells. See, e.g., Kamb, “Cell-Cycle Regulators and Cancer,” Trends in Genetics, vol. 11, 1995, pp.136-140; and Coleman, supra. In addition, changes in the expression of or in the genes encoding CDK's or their regulators have been observed in a number of tumors. See, e.g., Webster, “The Therapeutic Potential of Targeting the Cell Cycle,” Exp. Opin. Invest. Drugs, Vol. 7, pp. 865-887 (1998), and references cited therein. Thus, there is an extensive body of literature validating the use of compounds inhibiting CDKs as anti-proliferative therapeutic agents. See, e.g. U.S. Pat. No. 5,621,082 to Xiong et al; EP 0 666 270 A2; WO 97/16447; and the references cited in Coleman, supra, in particular reference no. 10. Thus, it is desirable to identify chemical inhibitors of CDK kinase activity.
It is particularly desirable to identify small molecule compounds that may be readily synthesized and are effective in inhibiting one or more CDKs or CDK/cyclin complexes, for treating one or more types of tumors.
Several classes of compounds that inhibit cyclin-dependent kinases have been and are being investigated as therapeutic agents. These are, for example, as follows:    Analogs of Flavopiridol:    U.S. Pat. No. 5,733,920 (Mitotix)    WO 98/1344 (Bristol-Myers Squibb)    WO 97/42949 (Bristol-Meyers Squibb)    Purine Derivatives:    WO 98/05335 (CV Therapeutics)    WO 97/20842 (CNRS)    Acridones and Benzothiadiazines:    WO 98/49146 A2 (US Dept. of Health and Human Services)    Antisense    U.S. Pat. No. 5,821,234 (Stanford University).
Furthermore, certain N,N-substituted dihydropyrazolobenzodiazepines have been disclosed in an article discussing CNS-acting compounds. See, M. A. Berghot, Arch. Pharm. 325:285-289 (1992).
There continues to be a need for easily synthesized, small molecule compounds for the treatment of one or more types of tumors, in particular through regulation of CDKs. It is thus an object of this invention to provide such compounds and compositions containing such compounds.